1. The Field of the Invention
The present invention relates to analyzing signals between a host and a device by tapping the bus. More particularly, embodiments of the invention relate to sampling the bus in preparation for analysis of data on the bus.
2. The Relevant Technology
Protocol analyzers are devices that help diagnose and detect problems that occur on networks. Typically, protocol analyzers view traffic on the network or over a bus as it occurs. As the data is being monitored, the protocol analyzer may detect a problem or some defined condition. At this point, the analyzer triggers and captures the data present on the network or on the bus. The amount of data captured can depend on the size of the analyzer's buffer. The analyzer can also be configured such that the captured data represents data that occurred before the triggering event, after the triggering event, and/or both before and after the triggering event. In addition, the data can also be captured without a triggering event. Rather, data can be captured until the buffer is full. In effect, the capture is a snapshot of the data that was present on the network or on the bus around the time that a problem occurred or around a time that the analyzer was triggered. The captured data can then be analyzed to help resolve many problems and improve network communications or to improve communications between a host and a device.
Some protocols, however, are difficult to implement in analyzers. SD (Secure Digital Cards), SDIO (SD Input/Output Cards), MMC (Multimedia Cards) and CE-ATA (Consumer Electronics-Advanced Technology Attachment) are examples of protocols that are difficult to analyze.
Some of the reasons are related to the physical sizes of devices that use SD, SDIO, MMC or CE-ATA. Other reasons are related to the cost. CE-ATA connectors, for example, have a limited duty cycle. Because protocol analyzers are repeatedly connected and disconnected, cost can become a significant issue when analyzing CE-ATA. In addition, many consumer devices do not operate at the same voltage levels. This can complicate the issue of connecting a system to a protocol analyzer when the voltage levels are not known beforehand because the analyzer may not be able to distinguish between low and high signals. Further, when the bus is electrical in nature rather than optical, there are also issues related to impedance matching and capacitive loading.